How to rewrite query

[Mindaugas]

  Hello,

  For the Radius server we're using MySQL cluster and the following query 
looks too slow:

select ip from ipaddr
  where pool='INTERNET' and stype='S' and ls_id=3 and allocated is null
  limit 1;

  Table ipaddr is small (~6MB, 38000 records). Fields in WHERE clause have 
few values and no indexes:
  - pool: 2 distinct values;
  - stype: 6 distinct values;
  - ls_id: 5 distinct values;
  - allocated is null for ~30000 of records.

  Table type is NDB. If I change it to MEMORY everything starts to fly.

  Of course there are a lot of updates to ipaddr table too. For every select 
there are 3 updates. But updates are of type "update something where 
ip=ipaddr" and ipaddr is unique key.

  What can cause slowdown in NDB case? Table is small and is in memory (5.0 
cluster). Maybe I can rewrite it in some better form for such case?
  MySQL setting are basically default. I did not find something in 
documentation about improving performance of NDB engine tables.
  Maybe increase read_buffer_size which is currently the default 128k? 
Server has 4GB of memory and runs x86_64 version of CentOS4 Linux.

  Thanks,

  Mindaugas